Protective arrangement for alternating electric current systems



June 9, 1925. 1,541,720 B. H. LEESON ET AL PROTECTIVE ARRANGEMENT FORALTERNATING ELECTRIC CURRENT SYSTEMS Filed Oct. 22, 1925 2 Sheets-Sheet1 F/GJ.

INVENTOR uc By 1 49 June 9, 1925. 1,541,720

8; H. LEESON ET AL V PROTECTIVE ARRANGEMENT FOR ALTERNATING ELECTRICCURRENT SYSTEMS Filed Oct. 22, 1923 2 Sheets-Sheet 2 IN VEN TOR PatentedJune 9, 1925.

nnrrso STATES PATENT OFFICE.

BRUCE HAMIER LEESON. OF TYNEMQUTH. AND REGINALD W'ILLIAM BILES, F BAL- 4COMDE. ENGLAND. ASSIGNORS TO ELECTRICAL IMPROVEMENTS LIMITED. OF NEW-CASTLE-UPON-TYNE, ENGLAND. A BRITISH COMPANY.

PROTECTIVE ARRKNGEMENT FOR AI ITERNATING ELECTRIC CURB ENT SYSTEMS-2.

Application iua October 22, 1923. sci-m1 No. 070,150.

To (17/ whom it may concern:

Be it. known that we, Banal-1 Hausa LEE- sox and REGINALD VILLIABIBruzs, subjects of the King of England; and residing. re spectively, at.'l vnemouth, Northumberland, England; and Balcombe; Sussex, En land,have invented certain new and usefu Improvements in Protective Arra'ements for Alternating: Electric Current ystems, of which he 1-.Jllowing is a specification.

This invention relates to protective arrangements foralternatingelectric current systems and has particular reference to rotectivedevices of the kind in which .It ere are superimposed upon the feedersor mains of an alternating current system; opposed E. M. F.s of afrequency ditferent (either higher or lower) from that of the mainsupply the tripping devices being! operated by a relay or otherfrequency discriminating device responsive only to the fru ucncy of thesuperimposed E. M. Ffs.

In protective arrangements of this general type as hitherto proposed thepower for generating the superimposed E. M. F.s

has been separate from the main supply but according to the presentinvention such power is derived from the main currentitself and isproportional thereto. Moreover the superimposed E. M. Ffs are normallybalanced, i. e., when the feeder or section is sound no current passesto the relays but on the occurrence ofa fault there is'an out of'balancecfl'ect the rcsulting current of a frequency ditl'erin; from the maincurrent being proportional to the fault current.

The power for generating the superimposed E. M. Ffs may be taken fromthe main system by means of small transformers.

The generation ofthe superimposed E. M. F.s and theirapplication to theconductors to heprotected may be accomplished in various ways of whichthe following are given as examples 2-- (a) By means of rotatingmachinery such as a synchronous motor supplied with current from themain system through transformers such motor working in conjunction witha frequency changer.

(b) By means of a vibrating member such as a tuning fork arranged withcontacts so as to interrupt the current from the trans former andsuperimpose on the system an E. M. F. of different frequency.

of an ionic transformer.

Preferred arrangements according to these.

.three methods areillustrated diagrammaticallyby way of example in theaccompanyin %drawiugs, in whichigure 1 shows a'n arrangement employmg asynchronousmotor coupled to a frequency changer,

Figure 2.1m arrangement employing a tuning fork, and

Ifigure 3 an arrangement employing an oscillatory circuit.

In Figure 1 the synchronous motor A is a driven by power derived fromtransformers on the main supply lines D. The motor A is coupled directlyto afrequency changer E which is supplied with current at normal linefrequency from transformers F and serves to superimpose on the lines D,through other windings on the same transformers F. E. M. F.s of afrequency different. from that. of the line. Asensitive relay Gcontrollingthe switches H is connected to the main conductors D throughtransformers J and is so adjusted that it will respond only to currentsat the frequency of the superimposed E. M. F.s and to a predeterminedvalue of such currents. K is a centrifugal contact making device mountedon the same shaft as the frequency changer E and the synchronous motorA. This device K prevents the superimposed E. M. F.s from being applieduntil the prescribed frequency has been obtained. An

exactly similar arrangement is provided at 'requency for thesuperimposed E. M. F.s and moreover the power available to act on therelays may be made as high as may be desired by suitably dimensioningthe synchronous motor. This makes it possible to employ low faultsettings.

The arrangement has, however, the disadvantage of leaving the systemunprotected from the moment of switching in to the time whensynchronismis reached and the relays are allowed to be operative. This difficultycan be met by employing overload devices to protect the line during thiseriod.

The arrangement shown in igure 2 only differs from that of Figure 1 inthe method of generating the superimposed E. M. F.s and the samereference letters are employed where applicable. Transformers L similarto those usually employed with the Merz: Price protective gear areemployed to supply current proportional to that in the line to a circuitM containing a tuning fork N, which is arranged to iuterru t the currentso plied to that circuit from a transformers 1 .1 at a definitefrequencycorresponding to its natural frequency of vibration. The forkis maintained in a state'of s chronous vibration by means of a smallblectro-magnetic device 0 energized from the transformers L. Thecurrents at the new frequency determined by the tuning fork N act ontransformers P to superimpose E. M. F.s at this frequency on'the lineconductors D. As in the mucus arrangement equal and opposite E. F.saresuperimposed on the line at the two ends of the section to be protected,and any out-of-balance effect between these E.' M. F. s resulting from afault will act This arrangement has the advantage ofavoidin the use ofrotating or vibrating auxiliaries, and also gives immediate protectionto the line after switching in. On

the other hand, accurate tuning of the .oscillatory circuit is necessaryto ensure that the opposed superimposed E. M. F .s arein phase with oneanother.

Owing to the fact that according to this invention the superimposedcurrents are derived from the main current or fault current flowing inthe main feeder, the superimposed current at one end of a.protectedsection will be reversed in direction on the occurrence of, say, a faultof earth in the middle of the section. The superimposed currents willtherefore assist one another and circulate through the main conductorso'as to operate relays tuned to their fregueney.

When several sections of a fee er are each 5 to be tected and that thesuperim osed E a? P a s are normally balanced.

It'is further to be understood that the improvtfi arrangements can beapplied sa to a three-phase feeder or .section in sucli a manner that afault in one phase will cause the cutting out of the whole feeder orsection.

What we claim as our invention and desire to secure by Letters Patent isthrough the transformers J on the relays G 1. In a protectivearrangement for an in o n theswitches H. alternating electriccurrent'system the com- Tl ii s arrangement allows practicallyinbination with the conductors of the system stantaneous protection tobe obtained from to be protected, of devices for generating the momj lifitswitchin in, provided that electro-motive-forces havin a frequencythe tuning f" k is ma e to operate more different from that of the mainsupply, quickly than the relay mechanism. means for supplying power fromthe mam Figure 3 illustrates a further alternative conductors to thegenerating-devices wheremethod of Igenerating the superimposed E. by thefrequency 0 the electro-motive-forces M. F.s. n' this arrangement )oweris generated bears definite synchronous relasupplied from eachline-conductor through tion to that of the main supply, means a smalltransformer Q of the Mel's-Price whereby the electro-motive-forcesgenerated type to an oscillatory circuit R containing a condenser S andthe primary winding of a transformer T. This circuit R generates highfrequenc oscillations which are su er imposed on the line. Thus normallyialanced M. F.s of high frequency are superi'm osed on the line, andcurrents at this requency resulting from an out-ofbalance effect due toafault act, as in the previous arrangements, through transformers J onthe relay G which controls the switrhes H. Small choke coils U areprovided as shown to prevent the high frequency oscillations fromreacting on the trans ormers Q.

by the generating devices are superimposed on the main conductors,circuit-breakers adapted when 0 erated to cut out the main conductors,an means whereby'the su er imposed electra-motive-forces are cans to I 0operate'the circuit-breakers when a. fault occurs.

2. In a protective arrangement for an alternating electric currentsystem the combination with the conductors of the system to beprotected, of a device'provided at each end of the system wherebyelectro-motiveforces are generated having a frequency different from butbearing a definite synchronous relation to that of the main supply,

transformers through which power derived from the main conductors issupplied to the generating devices, means whereby the electro-motiveforces generated by the !two devices are superimposed on the main'conductors in such a manner as to be opposed to one another,circuit-breakers adapted when operated to cut out the main conductors,and means whereby the superimposed electromotive-forces are caused tooperate the circuit-breakers when a fault occurs. 3. In 'a protectivearrangement for a alternating electric current system the combinationwith theconductors of the system to be protected, of devices forgenerating clectric-motive-foroes having a frequency different from thatof the main supply, means for supplying power from the main conductorsto the generating devices are superimposed on the main conductors suchsuperimposed electro-motiv'e-forces bein normally balanced,circuit-breakers adapted when 0 rated to cut out the maih conductors, reays controlling the circuit-breakers and sensitive only to thesuperimposed frequency and meanswhereby the out-of-balance ell'ect ofthe superimposed electro-motive-forces'due to the occurrence of a faultin the main conductors is operative to cause the relays to actuate thecircuit-breakers and thereby to cut out the main conductors. I

4. In a protective arrangement for an alternating electric currentsystem, the combination with the conductors of the system to beprotected, of a device provided at each end of the system wherebyelectro-mbtiveforces are generated having a frequencydifferent. from-butbearing a definite synchrm nous relation to that of the main supply,transformers through which power derived from the main conductors issupplied to the .generating devices, transformers throu h which theelectro-motive forces generated y the two devices are superimposed onthe main conductors such superimposed electromotive-forces bein opposedand normally balanced, circuitreakers adapted when operated to cut outthe main conductors, re-

lays controlling the circuit-breakers and sensitive only to thesuperimposed frequency, and means whereby the out-of-balance effect ofthe superimposed electro-motiveforces due to the occurrence of a faultin the main conductor is operative to cause the relays to actuate thecircuit-breakers and thereby to cut out the main conductors.

5. In a protective arrangement for an alternating electric currentsystem, the combination with the conductors of the system to beprotected, of tunedoscillatory serving to generate electro-motweforcescircuits motive-forces are caused to operate the cir-' cuit-breakerswhen a fault occurs.

6. In a protective arrangement for an alternating electric currentsystem, the combination with the conductors of the system to beprotected, of a tuned oscillatory circu-it provided at each end of thesystem whereby electro-motive-forces are generated having a frequencydifferent from that of the main supply, transformers through which poweris supplied from the main conductors to the oscillatory circuits, meanswhereby the electro-mot-ive-forces generated by the oscillatory circuitsare superimposed on the main conductors such superimposedelectro-motive-forces being normally balanced, circuit-breakers adaptedwhen operated to cut out the main conductors, and means whereby theout-of-balance effect of the superimposed electro-motive-forces due tothe occurrence of a fault is caused to operate the circuit-breakers andthereby to cut out the main conductors.

7.- A protective arrangement for an alternatin electric current systemincluding in combination at each end of the conductors of "the system tobe protected a tuned oscillator? circuit comprising capacities andinductances and serving to generate electro-mo tive-forces having afrequency difi'erent from v that of the main supply, transformersthrough which wer derived from the main current is supp ied to theoscillatory circuit,

transformers through which the generated electro-motive-forces aresuperimposed on the main conductors, a relay sensitive only to thesuperimposed frequency, switches in the main conductors ntrolled by therelay, and transformers thro gh which the relay is connected to the mainconductors, the arrangement bein such that the superimposedelectro-motiveorces supplied from the two ends of the system arenormally balanced but on the occurrence of. a fault there is anout-of-balance effect betweemth'efysuperimposed electro-motive-forcesresulting in a current which is proportional to the main fault currentand which acts on the relays to cause them to cut out the protectedconductors as set forth.

In testimony whereof we have signed our names to this specification.

BRUCE HAMER LEESON.

REGINALD WILLIAM BILES.

